Practitioners of aerospace medicine are responsible for the health and welfare of those involved in aviation and space operations. This includes civil aviation and military aviation, as well as ground support personnel such as air traffic controllers and maintenance workers. In recent years, commercial air travelers have also come under the purview of this specialty. Aviation medicine, which was the forerunner of aerospace medicine, has its origins in World War I. As we entered the space age, the specialty increased its breadth and became aerospace medicine as we know it today. Residency training is of two years' duration beyond PGYI, after which candidates may sit for board certification examination under the auspices of the American Board of Preventive Medicine. Most aerospace medicine specialists are affiliated with the Federal Aviation Administration (FAA), the National Aeronautics and Space Administration (NASA), the airlines, the military services, the aerospace industry, or in private consulting. With the predicted growth of aviation during the coming decade and the construction of the International Space Station, aerospace medicine will face many challenges in the coming century. The following is a brief overview of some of these challenging issues.
The most immediate and challenging issue today in commercial aviation is the question of U.S. air carrier in-flight emergency medical kits (EMK). In 1986, the FAA mandated that all U.S. air carriers will have onboard a first-aid kit and a EMK containing four medications: nitroglycerin tablets, diphenhydramine injectable, 50% dextrose, and 1:1000 epinephrine. A two-year study from 1986 to 1988 indicated that this kit was adequate1; hence, there was no further discussion until several years ago when there was a call by the media, the medical community, and Congress to resurrect the issue with an eye toward enlarging the kit contents. This was prompted by a number of in-flight medical events and deaths in which passenger physicians who were called upon to treat sick passengers in-flight complained that the EMK contents were inadequate. Some of these events received wide publicity in the press and in TV special features. One case that received international publicity was that of a woman on an international flight with a tension pneumothorax who was undoubtedly saved by a resourceful physician passenger who rigged a thoracostomy set utilizing a catheter, a coat-hanger, and a bottle of mineral water. In July 1996, the Chicago Tribune ran a special 16-page feature entitled "Survival in the Sky: Code Blue" that attracted widespread attention.
In May 1997 the U.S. House of Representatives' Subcommittee on Aviation held a special hearing calling upon aerospace medicine specialists to give testimony on the desirability of enhancing the FAA-mandated kit to include an onboard automatic external defibrillator (AED). Because of this hearing, the Aerospace Medical Association offered to study the entire issue and to bring forward its recommendations.
This task was particularly challenging because there is no comprehensive database containing the incidence of illness, including cardiac arrest, in-flight. Furthermore, there is no mandate requiring the airlines to report in-flight medical events. Articles in the literature are anecdotal, and far from comprehensive. Nevertheless the Aerospace Medical Association (AsMA) decided to make its recommendations based upon the information that was on hand.
Consequently, AsMA convened a task force in August 1997. Prior to the task force meeting, a survey was sent to 2,300 physician members of AsMA asking if they had ever treated a passenger in-flight, and if so, what was the presumed diagnosis or sign/symptoms. Based upon this survey, the available literature, and medical consensus of the group, recommendations, were made (Table 1), published, and forwarded to the Congress, the FAA, and the major airlines.
| Table
1. AsMA Task Force Recommendations for US Air Carrier Inflight Medical Kits |
|
| Acetaminophen Albuterol ASA Dextrose (50%) Diazapam Diphenhydramine Epinephrine Glucagon |
Lidocaine Meclizine Neosynephrine Nasal Spray Nitroglycerin Phenergan Simethicone Toradol |
Regarding AEDs, even though the incidence of in-flight cardiac arrest is unknown, the Task Force felt that the airlines should carry them at least on selected routes, particularly long haul, over-water. Qantas Airlines has been the only major airline to carry AEDs since 1991, during which time they were utilized 27 times in-flight with four firings, of which there were two saves..2 A number of other small airlines carry AEDs but nothing has been published regarding usage. American Airlines has carried onboard AEDs on long haul, over-water flights as of July 1997, with plans to place them eventually on all routes. Likewise, Delta and United Airlines have recently announced they would begin carrying them in the near future.
AEDs are small, easy to stow, and are semi-automatic, firing only when they detect ventricular fibrillation or rapid ventricular tachycardia. They will not fire in the event of other arrhythmias. Furthermore, training of flight attendants in their use is not problematical.
As the airlines enhance their EMKs and incorporate AEDs, the question of liability will certainly arise. Although at the time of this writing, there have been no suits filed in a U.S. court against physicians who allegedly mismanaged a sick or injured passenger, the potential is certainly there.3 For this reason, the Aerospace Medical Association has urged the House Aviation Subcommittee to consider an in-flight Good Samaritan law. H.R. Bill 2843, the Aviation Medical Assistance Act of 1997 by Congressman Duncan, has such language and is expected to reach the House floor in the coming months.
Another area of concern in civil aviation is cabin air quality. Cabin crew and passengers have registered a broad spectrum of complaints, including nausea, vomiting, headache, dizziness, fatigue, and menstrual disorders. Many believe that their symptoms are due to poor air quality and recirculated air. In addition, there have been several studies published of tuberculosis transmission from passenger-to-passenger and from flight-attendant-to-flight attendant. Consequently, the aircraft ventilation system has been impugned particularly because 50% of cabin air is recirculated.
Nevertheless, a number of in-flight studies of pollutants — carbon monoxide, carbon dioxide, oxygen, respiratory particulates, ozone, volatile organic compounds, and biologicals — have consistently demonstrated levels well below those set by regulatory agencies.4,5 Furthermore, no pathogens, bacterial or fungal, had been identified on cultures. The two cases of TB transmission have been attributed to being in a closed space and in proximity to the index case rather than to the aircraft ventilation system.6 Unfortunately, viral studies in-flight have not been done because the technology to do so has not been available. Clean air in aircraft cabins is most likely due to the employment of high-efficiency particulate airfilters (HEPA) in the ventilation system. Recirculated cabin air goes through the HEPA, which filters all particles that are .3 microns or larger. Only viral particles are smaller, but they tend to cluster in large clumps that are easily filterable. Nevertheless, to ensure that viral particles are not getting through the system, further studies must be done. For now the most effective way to prevent the transmission of disease in-flight is for physicians to advise would-be travelers who are ill to postpone travel.
It is most likely that the transmission of disease in-flight is due to an enclosed space rather than the aircraft ventilation system. The multiple complaints of cabin crew and passengers are probably not due to substandard cabin air quality, but rather to other features of flight, such as a lowered barometric and oxygen pressure, noise and vibration, fatigue, jet lag, airport tumult, and other such factors.
American astronauts and Russian cosmonauts have established a presence in space for approximately 40 years. Although most have several weeks in space, a few have logged a little over one year. Based upon this experience, scientists and flight surgeons have defined the physiological effects of microgravity and readaptation upon return to Earth.7 Although astronauts upon return have complete recovery from the effects of microgravity, we do not know how crewmembers will fare on long-duration missions to Mars, of two or three year's duration. Although a number of countermeasures have been under investigation, they only retard the effects of microgravity; none has proved to be truly effective. Consequently, considerable research must be accomplished if we plan to remain in space for longer periods. One promising area of research is artificial gravity provided by a rotating space vehicle or in-flight small arm centrifuge. By imposing gravitational forces in-flight, there is the possibility that the adverse effects of microgravity — cardiovascular, musculoskeletal, and neurovestibular — might be ameliorated or even fully prevented.
Following the tragic earthquake in Armenia about 10 years ago, NASA offered assistance in the form of telemedicine consultation utilizing audio/video and facsimile in real time via landlines and satellite. Four medical centers in the United States were linked to a medical facility in Yerevan Armenia allowing U.S. Consultants to communicate with Armenian colleagues regarding medical care of the casualties. Although NASA's offer was based upon humanitarianism, the project also served as a test bed for the utilization of telemedicine in space. This is an extremely important medical modality for the space program in that medical care, particularly on long-duration missions, could be administered by physicians on the ground, thereby possibly obviating not only crew morbidity in-flight or even death, but also avoidance of aborting a flight at great taxpayer expense. NASA continues to test its telemedicine systems via a Space Bridge to Russia through which Russian and American physicians at designated medical centers conduct real-time patient consultations as well as medical education programs.
NASA has recently developed a telemedicine instrumentation package (TIP) with the capability of transmitting vital signs, pulse oximetry, ECG, otoophthalmoscopy, and other diagnostic options. The TIP was successfully flown on a Shuttle mission in January 1998. NASA's development of telemedicine technology is a major contribution to this new science in the care of patients on Earth.
In addition to telemedicine, there have been other significant life sciences spin-offs. For example, angioplasty can now be employed in nonsurgical removal of artheromatous plaques. This technology was derived from instruments utilized to measure gases in the Earth's atmosphere. Cardiac imaging for balloon angioplasty was originally developed for satellites to survey Earth's resources. The advanced implantable pacemaker with an electronics package allowing reprogramming without surgery. And finally, a rapid heat transfer technique for sterilizing medical instruments within six minutes was developed from a system designed to sterilize space vehicles potentially contaminated after a Mars mission.
Because flying safety is paramount in civil aviation, great caution is necessary in medication prescribed for aviators. This includes not only airline pilots but also pilots in general aviation who fly for pleasure. For example, medications that cause drowsiness or changes in mentation are usually disqualifying because they pose a threat to flying safety. However, as experience has been accrued over the years, there has been a slow deliberative trend toward more liberal ground. As an example, the FAA has just begun approving special issuances (re: waivers) for selected general aviation pilots on insulin for diabetes mellitus (airline pilots at the time of this writing are excluded from this policy). In order to prevent hypoglycemic effects, only well-controlled individuals are granted the special issuances. Furthermore, they must adhere to specific procedures (glucometer testing preflight and in-flight) and ensure regular follow-up by their physician.
Like their civilian aviation counterparts, military aircrew may be disqualified for illness or for medication prescribed. This is especially compelling for aircrews subject to accelerative forces (G) and hypoxic conditions. If medication is prescribed, it must not have unwanted side effects such as drowsiness or cause performance decrement in a stressful environment. Until recently, only certain diuretics for hypertension had been approved. However, in order to give flight surgeons more treatment options for aviators with hypertension, an ACE inhibitor (lisinopril) is now approved in selected cases. This policy change was implemented after having tested a number of aircrew on the medication in simulated flight in a human centrifuge and altitude chamber to ensure there were no unwanted side-effects or performance decrement.
Another challenge to aerospace medicine is crew protection, particularly headward acceleration imposed upon aircrew by high performance aircraft. High G forces (up to +9 G) causes a decreased blood flow to the brain and loss of consciousness (referred to as GLOC). G-lock is a significant threat to flying safety with a number of aircraft lost due to its effects. Crewmembers protect themselves with anti-G maneuvers such as forceful exhalation through a partially closed glottus and anti-G suits. A relatively new protective ensemble is anti-G suit combined with increased intrathoracic pressure utilizing oxygen delivered via the aviator oxygen mask. These techniques are protective because they maintain blood pressure above the heart and increase venous return and cardiac output thereby reducing the risk of GLOC.
The effect of high-G exposure over a professional lifetime on the cardiovascular system of fighter pilots is undefined. Although autopsies during the Korean War era on fighter pilots and animal studies indicate no ill effects, this does not necessarily exonerate the modern high-performance aircraft of today that imposes much higher G forces than those of 40 years ago. Although recent echocardiographic studies of pilots suggest that accelerative forces do not damage the structural integrity of the heart, more studies will be necessary if we are to have 100% certitude as newer and higher performance aircraft capable of +12 G acceleration enter the military inventory.8
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